1. Field of the Invention
This invention relates to an inscribed meshing planetary gear construction which is preferably applied to a speed increasing gear or a reduction gear, more particularly, a small-sized speed increasing gear or a reduction gear in which a high output is required.
2. Description of the Prior Art
In the prior art, it is widely known to provide a speed increasing gear or a reduction gear employing an inscribed meshing planetary gear construction comprising a first shaft, an external-tooth gear assembled on the first shaft through a eccentric body in a state where the external-tooth gear can be rotated eccentric around the first shaft, an internal-tooth gear with which the external-tooth gear is inscribed and meshed, and a second shaft connected to the external-tooth gear through means for transmitting only the rotation component of the external-tooth gear.
An example of the prior art of this construction is shown in FIGS. 9 and 10. This prior art is constructed such that said first shaft is considered as an input shaft, said second shaft is considered as an output shaft and at the same time said construction is considered to a reduction gear by fixing the internal-tooth gear.
Eccentric bodies 3a, 3b are fitted on to the input shaft 1 with a predetermined phase difference (180.degree. in this example). The eccentric bodies 3a, 3b are integrated into one body. Two external-tooth gears 5a, 5b are placed on to each of these eccentric bodies 3a, 3b through eccentric bearings 4a, 4b. A plurality of inner roller holes 6 are provided in the external-tooth gears 5a, 5b. Also, an inner pin 7 and inner roller 8 are fitted in these roller holes.
A main object of providing two external-tooth gears (plural rows) is to increase a transmittance capacity, maintain a strength and keep a rotational balance.
External teeth 9 such as trochoidal or circular teeth etc. are provided at outer circumferences of said external-tooth gears 5a, 5b. The external teeth 9 are inscribed and meshed with the internal-tooth gear 10 fixed to the casing 12. The internal teeth of the internal-tooth gear are constructed such that an outer pin 11 is loosely fitted to an inner pin hole 13 to allow rotation of outer pin 11.
The inner pin 7 passing through said external-tooth gears 5a, 5b is tightly fitted or fixed to flange 14 of the output shaft 2.
When the input shaft 1 is rotated once, in conjunction the eccentric bodies 3a, 3b rotates once. The external-tooth gears 5a, 5b are apt to in an oscillating manner rotate on an eccentric axis around the input shaft 1 through this one revolution of the eccentric bodies 3a and 3b. However, since the rotation is restricted by the internal-tooth gear 10, the external-tooth gears 5a, 5b almost perform eccentric rotation while being inscribed with the internal-tooth gear 10.
Now, it is assumed that the number of teeth of the external-tooth gears 5a, 5b is N and the number of teeth of the internal-tooth gear 10 is N+1, then the difference between the numbers of teeth is 1. Consequently, the external-tooth gears 5a, 5b are displaced by one tooth relative to the internal-tooth gear 10 fixed to the casing 12 every time the input shaft 1 is rotated. This means that one revolution of the input shaft 1 is decelerated to a revolution of -1/N (-indicates opposite direction of input shaft of the internal-tooth gear.
Oscillation component of the external-tooth gears 5a, 5b is not transmitted due to the clearances between the inner roller holes 6 and the inner rollers 9 and then only the revolution component is transmitted to the output shaft 2 through the inner pins 7.
In this case, the inner roller holes 6a, 6b, inner pins 7 and inner rollers 8 form an "isokinetic inscribed meshing mechanism".
As a result, finally, a reduction of reduction ratio -1/N can be accomplished.
In the example of this prior art, the internal-tooth gear of the inscribed meshing planetary gear construction is fixed, the first shaft is an input shaft and the second shaft is an output shaft. However, a reduction gear can also be constructed by fixing the second shaft and applying the first shaft as an input shaft and the internal-tooth gear as an output shaft. Furthermore, a speed increasing gear can also be constructed by reversing these inputs and outputs.
As described above, the inner pin 7 has a function to form an circular tooth acting as one of elements of said "isokinetic inscribed meshing mechanism" constructed with the inner roller holes 6a, 6b, and also has another function acting as a carrier member for transmitting a rotational force of a rotation of external-tooth gears 5a, 5b to the output shaft 2. In particular, in order to keep a superior former function, it was essential to provide the inner rollers 8 capability of freely rotating around the inner pins 7. The inner roller 8 shows a problem of expensive cost due to the fact that the material must be hard both outer and inner circumferences there for must be coaxially and accurately machined (processed or manufactured).
In view of this fact, an idea has been proposed that the function which forms a circular tooth of one of the elements of the "isokinetic inscribed meshing mechanism" and another function which acts as a carrier member for transmitting a rotational force of the external-tooth gears 5a, 5b to the output shaft 2 are separated, and even if the inner roller 8 is eliminated, it has a similar performance to that of having the inner roller 8. This structure is illustrated in FIGS. 11 and 12.
This structure comprises, as means for transmitting a rotational component of the external-tooth gears, the inner pin 7 arranged in the external-tooth gears 5a, 5b, an annular support ring 17 receiving a rotation corresponding to the rotational component of the inner pin 7 (the rotational component of the external-tooth gears), and a carrier pin 16 projected from the flange 14 formed at the output shaft 2, connected and fixed to the support ring 17.
Said inner pin 7 is rotatably assembled to the flange part 14 and the support ring 17 through bushes 18a, 18b. That is, since the inner pin 7 is not necessarily tightly connected to the output shaft 2 due to the presence of the carrier pin 16, it can be constructed to be rotatable, resulting in that the prior art inner roller 8 can be eliminated. Said annular support ring 17 is assembled to an extremity end portion of said carrier pin 16. Since the carrier pin 16 only has a function to transmit a rotational force of the support ring 17 to the output shaft 2, there are provided through-holes 20a, 20b which do not contact with the carrier pin 16 even if the carrier pin 16 oscillates at the corresponding portion on the external-tooth gear 5a, 5b.
Incidentally, in FIG. 11, reference numerals 15a, 15b denote bearings of the output shaft 2. Reference numeral 21 denotes an inner pin retainer plate for determining an axial position of the inner pin 7. Reference numeral 23 denotes an inner pin retainer plate bolt. Reference numeral 22 denotes a steel plate race.
However, as apparent from FIGS. 9 and 11, a prior art reduction gear was constructed such that a variation in load generated at the reduction mechanism and/or external radial load from a mating machine acting against the output shaft 2 is supported by a pair of bearings 15a, 15b, resulting in that in order to increase a supporting stability, it was necessary to extend the Y segment and shorten the X segment in FIGS. 9 and 11 as much as possible.
However, since it was difficult to shorten the X segment, the Y segment had to be necessarily elongated, resulting in that it had a problem that an axial length of the reduction gear was elongated.
Then, as shown in FIG. 13, it had also been proposed to have a structure in which "a shoulder" 71 and a threads 72 machined at both ends of the inner pin 7A, the annular support ring 17A is integrally formed with the input shaft 1A, the supporting ring 17A and the flange part 14A of the output shaft 2A are connected and fixed by a nut 73, and the reduction mechanism is disposed between the flange part 14A of the output shaft 2A and the support ring 17A (Jap. U. M. Pub. No. Sho 31-9414).
However, such a supporting construction has been constructed such that the shoulder and the threads are machined at the inner pin which is required increased-hardness and an accuracy so as to be threaded engaged with the input shaft and to be fixed to the flange part, and the nut is fastened. Therefore, it has some disadvantages that the machining accuracy or assemblying accuracy is difficult to attain, and the cost is excessively high. Furthermore, the load concentrated at the shoulder section which effect both supporting structures is eliminated, and another countermeasure for preventing loosing of the plate is required whereby a structure is extremely complex. Therefore, the fact is that this prior art structure (FIG. 13) is no comparison for said structure shown in FIGS. 11 and 12.